Electron paramagnetic resonance (EPR) will be employed to probe the interaction of divalent cations with biological membranes and model membranes. Mn2 ions is the optimal ion for these studies both because of its close chemical similarity to the physiologically important cations, Ca2 ion and Mg2 ion, and because of its desirable EPR properties. One example to be studied in great detail is the binding of Mn to negatively charged phospholipid vesicles. The influence of polar head groups, monovalent salts, temperature and added perturbing agents (local anesthetics, neurotransmitter, detergent, etc.) will be examined. Binging to cation exchanges with the surface carboxyl or sulfonate groups will also be measured with EPR. One aim will be to establish methodology for distinguishing spectrally between Mn ions held in a diffuse double layer and those actually complexed to a surface. Divalent cation (Ca2 ion and Mn2 ion) transport by rat liver mitochondria is also being studied. Recent work from this laboratory has provided strong evidence for a separate efflux mechanism, insensitive to the powerful Ca uptake inhibitor, Ruthenium Red. The efflux system will be investigated by observing what factors influence the rate of divalent cation release from preloaded mitochondria, when unidirectional influx is blocked by EGTA or Ruthenium Red. BIBLIOGRAPHIC REFERENCES: J.S. Puskin. Divalent Cation Binding to Phospholipids: An EPR Study. J. Memb. Biol. (in press: July, 1977). J.S. Puskin, T.E. Gunter, K.K. Gunter and P.R. Russell. Evidence for More Than One Ca 2 ion Transport Mechanism in Mitochondria. Biochemistry 15 (1976) 3834-3842.